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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Significant power loss caused by the Phantom concentric tube silencer.

Identifier  ExFiles\Box 66\2\  scan0093
Date  22th September 1925
  
COPY.
BJ.
OWB10/LH{Mr Haworth}22.9.25.

PHANTOM EXHAUST. CONCENTRIC TUBE SILENCER.

It is considered that in view of the obvious advantages of this silencer over the present standard, as regards the quietness of the car, both when standing (to outside observers) and when running (to outside observers and to the occupants) we should standardise this until such time as we can produce a silencer equally efficient, as regards silence, but which absorbs considerably less power at the higher speeds.

The loss of power with this silencer is very considerable and is considered an unnecessary tax upon the engine. It must materially reduce the performance - using 'performance' in its broadest sense - at all car speeds of more than 50 mph. It must materially increase the petrol consumption at all speeds above 50 mph.

From the curve you have provided with Hs{Lord Ernest Hives - Chair}3/LG11.9.25, the losses are as follows - in each case at full throttle and engine revolutions corresponding to speeds in Column 1 :-

Speeds in m.p.h. H.P. lost at road wheels. Percentage H.P. lost of power developed at road wheels.

49. 5.5. 7.1
56. 10.5. 12.4
63. 16. 17.8
70. 20. 22.8
77. 28.5. 28.

These figures appear to show that we are paying a very severe price for silence. Is this necessary?

(sgd.) CWB.
  
  


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